Process of delustering and then completely saponifying cellulose ester filaments



United States Patent PROCESS OF DELUSTERING AND THEN COM- PLETELY SAPONIFYING CELLULOSE ESTER FILAMENTS William Whitehead, Forest Hills, N. Y., and Linus M.

Heming, Cumberland, Md., assignors to Celanese Corporation of America, New York, N. Y., a corporation of Delaware No Drawing. Application July 13, 1953, Serial No. 367,762

7 Claims. (Cl. 8-129) This invention relates to materials of subdued luster and relates more particularly'to saponified stretched cellulose ester yarns having a subdued luster.

It has long been the practice to deluster artificial filaments, such as filaments made of cellulose ester or regenerated cellulose, by the incorporation of certain pigments, e. g. titanium dioxide, in the spinning solutions from which such filaments are made. When it is attempted to deluster saponified stretched cellulose ester yarns in this manner, it is found that the use of such a pigment is fairly effective, although expensive, if a chalky effect is desired.' However, when the amount of pigment is reduced in order to produce a filament of subdued luster, rather than a chalky filament, the results are unsatisfactory. More particularly, it is difficult to disperse the small amounts of pigment throughout the filaments with sufiicient uniformity, and the resulting filaments therefore have an undesirable streaky appearance.

It is therefore an object of our invention to provide a novel, economical and eflicient process for the production of permanently delustered saponified stretched cellulose ester materials in filamentary form.

Another object of our invention is the provision of a new process for producing a saponified stretched cellulose ester yarn having a subdued luster.

A further object of our invention is to provide a novel saponified stretched cellulose ester in filamentary form, which saponified material is resistant to treatments which usually cause relustering.

Other objects of this invention will be apparent from the following detailed description and claims.

According to our invention, a lustrous, previously stretched filamentary material, e. g. a stretched yarn made of a cellulose ester, is treated with an aqueous medium at a temperature of at least about 90 C. in order to deluster said stretched yarn, following which the delustered yarn is treated with a saponifying agent to convert the cellulose ester into a regenerated cellulose. The resulting saponified yarn, which has a desirable high tenacity and a subdued luster, is resistant to treatments which ordinarily cause relustering of cellulose ester yarns which have been delustered by treatments with an aqueous medium at or near its boiling point.

The yarn being treated is preferably made of a cellulose ester of a carboxylic acid having 2 to 4 carbon atoms, such as cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate-propionate or cellulose acetatebutyrate. Optimum results are obtained with cellulose acetate yarn. The stretched yarn may be produced, in a manner well known in the art, by extruding a solution of the cellulose ester, e. g. a solution of cellulose acetate in acetone, through a spinnerette in the form of filaments, removing the solvent, and then stretching the resulting material to at least about 4 times its original length in the presence of a stretch-assisting agent such as steam or hot water. Best results are obtained when the material is stretched to about 6 to 10 times its original length in the presence of saturated steam under pressure, e. g.

2,776,869 Patented Jan. 8, 1957 saturated steam at a temperature of about 140 to 150 C. However, the degree of stretch may be much higher, for example, 20 times the original length, if desired. The stretched material may also be produced in a known manner by extruding the solution of the cellulose ester into a spin bath which is a coagulant and -a swelling agent for said solution and effecting the stretching of the coagulated filament in said bath to the degree indicated above. These stretching processes cause the molecules of the cellulose ester to become highly oriented along the fiber axis so that on saponification of the stretched cellulose ester there is produced a high-tenacity regenerated cellulose material which does not greatly decrease in tenacity when wet; for example, a regenerated cellulose yarn whose wet tenacity is about 80 to 90%, e. g. 86%, of its dry tenacity.

As stated, after the cellulose ester yarn has been stretched it is delustered by treating it with an aqueous medium at a temperature of at least about 90 C. However, the time required to suitably deluster the stretched material is relatively long when temperatures of about 90 C. are employed. Accordingly, for practical purposes the temperature of the aqueous medium should be at least about 98 'C. Temperatures above about 100 C. may be employed, but the aqueous medium generally must be maintained under pressure at these temperatures. The delustering action may be accelerated by using an aqueous medium whose pH is either on the alkaline or the acid side of a pH of about 5.8. It is preferable that the pH be greater than about 5.8, advantageously greater than 7, since the subsequent saponification step is generally carried out with a relatively strong alkaline solution and the use of an alkaline delustering medium is more compatible with such a saponification step. However, the delus'tering medium should not be too alkaline, since strongly alkaline solutions, e. g. an aqueous solution containing 0.6% caustic soda and 8% sodium acetate, when applied at the desired delustering temperatures, weaken the yarn to a considerable extent. Ac cordingly, it is desirable to use aqueous solutions containing only weakly alkaline materials, such as soap, so-

dium citrate, sodium acetate and the like, for the delustering treatment. If desired, other delustering agents may be present in the aqueous medium, e. g. small amounts of phenols or pine oil. The delustering solution should be applied for the period of time necessary to obtain substantial delustering of the yarn. Generally a period of about 10 or 15 minutes is sufiicient to obtain the desired effect. Little or no saponification of the cellulose ester takes place during the delustering treatment.

After the stretched cellulose ester yarn has been de lustered it is saponified, in a manner well known in the art, to form a regenerated cellulose yarn of high tenacity. Advantageously, the saponifying medium is aqueous and contains a suitable alkaline saponifying agent, such as sodium hydroxide, sodium carbonate or ammonium hydroxide. The medium may also contain a buffering agent, such as, for example, sodium acetate, sodium citrate, or sodium sulfate to produce a more uniform saponification. It is often desirable to use the same Weakly alkaline buttering agent in the delustering solution as in the saponification medium, so that when the saponification medium comes in contact with yarn wet with the delustering solution no extraneous materials will be introduced into said saponification medium. For optimum results the saponification should be effected at an elevated temperature which reduces the time necessary therefor.

One advantageous method of carrying out the treatment of the stretched cellulose ester yarn is to wind said yarn in the form of a package on a perforated core. The delustering medium is then forced from within the core through the perforations and through the windings of the yarn package, following which the saponifying medium is forced through the yarn package inthe same manner.

While this invention has been described primarily in connection with the treatment of yarn, it is to be understood that it is applicable to textile materials in general; For example, a woven or knitted fabric composed of stretched cellulose ester filaments may be delustered and saponified according to the same procedure as described above in connection with yarns.

In order to illustrate our invention further, the following examples are given:

Example I An 80-filament yarn of cellulose acetate having a denier of about 768 is stretched to about eight times its length in the presence of saturated steam under pressure at a temperature of about 145 C. to produce a yarn having a denier of 96, and the resulting stretched yarn is wound. ontoa cylindrical stainless steel core provided with numerous evenly distributed circular perforations in the same manner for minutes to effect complete hydrolysis of the cellulose acetate yarn. This saponifying solution contains 0.6% by weight of caustic soda and 8% by weight of sodium acetate and is at a temperature of C. Thereafter the yarn is washed by forcing water at a temperature of 30 C. through the windings. Part of the water is. removed from the yarn by vacuum applied through the perforated spindle, following which the yarn package is removed from the spindle and dried in an oven. The resulting yarn has a subdued luster, increased covering power, and'an improved hand, as compared with a yarn treated in an identical manner except that the delustering treatment is omitted. The delustered yarn has a tenacity of 6.8 grams per denier and an elongation of 6.0%. When the delustering treatment is omitted, the lustrous yarn has a tenacity of 7.0 grams per denier and an elongation of 6.0%.

Example II Example I is repeated with the exception that the water is at a temperature of 100 C. instead of 98, C. The resulting yarn is more delustered than the yarn of EX- ample I but has substantially the same tenacity and elongation characteristics.

Example III Example lllis repeated except that the temperature of the soap solution is 100 C. The tenacity and elongation ofthe resulting yarn are substantially the same as in Example III but the delustering is even more pronounced.

Example V Example I is repeated except that an aqueous solution containing about 7% of sodium acetate at a temperature of 98 C. is employed for the delustering step. The results are similar to those obtained in Example III.

The delustered appearance of the yarns obtained in accordance with Examples I to V is substantially unaffected by pressing, by damp ironing, or by treatment with organic solvents or swelling agents for cellulose acetate. The delustered yarns also have an improved hand as compared with similar yarns which have not been subjected to the delustering treatment.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the production of permanently delustered filamentary materials which comprises delustering an oriented cellulose ester of a carboxylic acid filamentary material by subjecting said material to the action of an aqueous delustering medium at a temperature of about to C. and then substantially completely saponifying said material in aqueous alkali, said aqueous delustering medium being an aqueous alkaline solution of insufficient alkalinity to substantially saponify said cellulose ester, said carboxylic acid being a fatty acid of 2 to 4 carbon atoms, and said filamentary material having been oriented by stretching it to at least 4 times its original length prior to said delustering treatment.

2. Process for the production of permanently delustered filamentary materials which comprises delustering an oriented cellulose acetate filamentary material by subjecting said material to the action of an aqueous delustering medium at a temperature of about 90 to 100 C. and then substantially completely saponifying said material in aqueous alkali, said aqueous delustering medium being an aqueous alkaline solution of insufiicient alkalinity to substantially saponify said cellulose acetate, and said filamentary material having been oriented by stretching it to at least 4 times its original length prior to said delustering treatment.

3. Process of claim 2 in which the temperature of the delustering medium is about 98 to 100 C.

4. Process of claim 2 in which the delustering medium is an aqueous solution of soap.

5. Process of claim 4 in which the temperature of said solution is about 98 to 100 C.

6. Process of claim 2 in which the delustering medium is an aqueous solution of sodium acetate.

7. Process of claim 6 in which the temperature of said solution is about 98 to 100 C;

References Cited in the tile of this patent UNITED STATES. PATENTS 1,984,788 Ellis et al. Dec. 18, 1934 2,072,250 Dreyfus Mar. 2, 1937 2,308,511 Hilliard Ian. 19, 1943 FOREIGN PATENTS 438,656 Great Britain Nov. 12, 1935 

1. PROCESS FOR THE PRODUCTION OF PERMANENTLY DELUSTERED FILAMENTARY MATERIAL WHICH COMPRISES DELUSTERING AN ORIENTED CELLULOSE ESTER OF A CARBOXYLIC ACID FILAMENTARY MATERIAL BY SUBJECTING SAID MATERIAL TO THE ACTION OF AN AQUEOUS DELUSTERING MEDIUM AT A TEMPERATURE OF ABOUT 90* TO 100*C. AND THEN SUBSTANTIALLY COMPLETELY SAPONIFYING SAID MATERIAL IN AQUEOUS ALKALI, SAID AQUEOUS DELUSTERING MEDIUM BEING AN AQUEOUS ALKALINE SOLUTION OF INSUFFICIENT ALKALINITY TO SUBSTANTIALLY SAPONIFY SAID CELLULOSE ESTER, SAID CARBOXYLIC ACID BEING A FATTY ACID OF 2 TO 4 CARBON ATOMS, AND SAID FILAMENTARY MATERIAL HAVING BEEN ORIENTED BY STRECTHING IT TO AT LEAST 4 TIMES ITS ORIGINAL LENGTH PRIOR TO SAID DELUSTERING TREATMENT. 